High-efficiency silicon solar-cell design and practical barriers

A numerical evaluation technique is used to study the impact of practical barriers, such as heavy doping effects (Auger recombination, band gap narrowing), surface recombination, shadowing losses and minority-carrier lifetime (Tau), on a high efficiency silicon solar cell performance. Considering a high Tau of 1 ms, efficiency of a silicon solar cell of the hypothetical case is estimated to be around 29%. This is comparable with (detailed balance limit) maximum efficiency of a p-n junction solar cell of 30%. Value of Tau is varied from 1 second to 20 micro. Heavy doping effects, and realizable values of surface recombination velocities and shadowing, are then considered in succession and their influence on cell efficiency is evaluated and quantified. These practical barriers cause the cell efficiency to reduce from the maximum value of 29% to the experimentally achieved value of about 19%. Improvement in open circuit voltage V sub oc is required to achieve cell efficiency greater than 20%. Increased value of Tau reduces reverse saturation current and, hence, improves V sub oc. Control of surface recombination losses becomes critical at higher V sub oc. Substantial improvement in Tau and considerable reduction in surface recombination velocities is essential to achieve cell efficiencies greater than 20%

Sensitivity analysis of add-on price estimate for select silicon wafering technologies

The cost of producing wafers from silicon ingots is a major component of the add-on price of silicon sheet. Economic analyses of the add-on price estimates and their sensitivity internal-diameter (ID) sawing, multiblade slurry (MBS) sawing and fixed-abrasive slicing technique (FAST) are presented. Interim price estimation guidelines (IPEG) are used for estimating a process add-on price. Sensitivity analysis of price is performed with respect to cost parameters such as equipment, space, direct labor, materials (blade life) and utilities, and the production parameters such as slicing rate, slices per centimeter and process yield, using a computer program specifically developed to do sensitivity analysis with IPEG. The results aid in identifying the important cost parameters and assist in deciding the direction of technology development efforts

Price estimates for the production of wafers from silicon ingots

The status of the inside-diameter sawing, (ID), multiblade sawing (MBS), and fixed-abrasive slicing technique (FAST) processes are discussed with respect to the estimated price each process adds on to the price of the final photovoltaic module. The expected improvements in each process, based on the knowledge of the current level of technology, are projected for the next two to five years and the expected add-on prices in 1983 and 1986 are estimated

Sensitivity analysis of the add-on price estimate for the silicon web growth process

The web growth process, a silicon-sheet technology option, developed for the flat plate solar array (FSA) project, was examined. Base case data for the technical and cost parameters for the technical and commercial readiness phase of the FSA project are projected. The process add on price, using the base case data for cost parameters such as equipment, space, direct labor, materials and utilities, and the production parameters such as growth rate and run length, using a computer program developed specifically to do the sensitivity analysis with improved price estimation are analyzed. Silicon price, sheet thickness and cell efficiency are also discussed

Sensitivity analysis of the add-on price estimate for the edge-defined film-fed growth process

The analysis is in terms of cost parameters and production parameters. The cost parameters include equipment, space, direct labor, materials, and utilities. The production parameters include growth rate, process yield, and duty cycle. A computer program was developed specifically to do the sensitivity analysis

Silicon based IR filters

The design and fabrication of silicon based IR (Infrared) filters for high-speed optical communication systems are the topic of this thesis. Its novelty is in two aspects: 1) Use of silicon wafers as an optical guiding medium; 2) Use of wafer bonding technique to attach two optical elements together. The structure consists of two optical waveguides, the bus waveguide and the drop channel waveguide. A ring on top of these waveguides couples them in such a way that only one narrow spectral line is removed from the bus waveguides which propagates in the dropchannel waveguide. The assembly is fabricated using waferbonding technique in silicon. A precise control over the waveguide dimensions, the ring dimensions and the distance between the ring and the waveguide is required for a specific spectral line to be coupled to the dropchannel waveguide. It is hoped that the use of VLSI technologies in fabricating optical elements may therefore advance the area of optical networking and sensing

SUPERNATANT PROTEIN FACTOR: INSIGHTS INTO ITS REGULATION AND ABILITY TO STIMULATE CHOLESTEROL SYNTHESIS IN VITRO AND IN CELL CULTURE

Supernatant protein factor (SPF) is a 46-kDa cytosolic protein that stimulates squalene monooxygenase, which catalyses the second committed step in cholesterol biosynthesis. The mechanism by which SPF stimulates this enzyme is not understood and the goal of these studies was to see if SPF affected cholesterol synthesis in cultured cells. Rat supernatant protein factor-like protein (SPF2) shares 77% sequence identity with human SPF. In my studies SPF2 also stimulated squalene monooxygenase in vitro and incubation of SPF2 with protein kinase A (PKA) and C increased its activity by about 2-fold, as shown earlier with SPF. GTP and GDP prevented the stimulation of squalene monooxygenase by SPF2, suggesting that binding of these nucleotides inhibits SPF2. This inhibition could be prevented by the addition of -tocopherol, although -tocopherol alone had no effect on SPF2 activity in vitro. Expression of human SPF in hepatoma cells, which lack expression of endogenous SPF, increased cholesterol synthesis by 2-fold and addition of dibuytrylcAMP, a PKA activator, to these cells yielded an additional 62% increase whereas addition of a PKA inhibitor completely blocked the ability of SPF to stimulate cholesterol synthesis. To further confirm a role for phosphorylation in the regulation of SPF, substitution of alanine for serine-289 (a putative PKA recognition site) reduced the PKA-mediated activation of SPF in vitro by 50%, as measured with microsomal squalene monooxygenase and completely blocked the ability of SPF to stimulate cholesterol synthesis in hepatoma cells. In further structure-function studies, deletion of the carboxy-terminal Golgi-dynamics domain greatly increased the ability of SPF to stimulate squalene monooxygenase in microsomes, but, paradoxically prevented SPF from stimulating cholesterol synthesis in cell culture. Addition of brefeldin A, which disrupts Golgi formation, also abolished the ability of SPF to stimulate cholesterol synthesis, supporting a role for the Golgi in SPF function. Since squalene monooxygenase is not thought to be rate-limiting with regard to cholesterol synthesis, the possibility that SPF might stimulate other enzymes in the cholesterol biosynthetic pathway was investigated. The substitution of 14Cmevalonate for 14C-acetate completely blocked an SPF-induced 1.5-fold increase in squalene synthesis, suggesting that SPF stimulated mevalonate synthesis at HMGCoA reductase. 2,3-Oxidosqualene synthesis from 14C-mevalonate remained elevated (1.3-fold) with mevalonate demonstrating that SPF also stimulated squalene monooxygenase in hepatoma cells. SPF did not increase HMG-CoA reductase or squalene monooxygenase enzyme levels in cells, indicating that SPF directly activated these enzymes. Indeed, addition of purified recombinant SPF to rat liver microsomes stimulated HMG-CoA reductase by about 1.5-fold. These results reveal that SPF directly stimulates HMG-CoA reductase, the rate-limiting step of the cholesterol biosynthetic pathway, as well as squalene monooxygenase, and, coupled with the ability of PKA-mediated phosphorylation to regulate SPF activity, suggest a new means by which cholesterol synthesis can be rapidly modulated in response to hormonal and environmental signals

Sensitivity analysis of high-efficiency silicon solar-cell design parameters

Silicon solar cell design parameters were investigated to determine their bearing on cell efficiency. Among the parameters reviewed were: (1) bulk resistivity, (2) minority carrier lifetime cell thickness, (3) front junction depth, (4) front surface doping concentration, (5) front surface recombination velocity, and (6) back surface contact. The following were concluded: (1) there is good agreement between experimental and simulation results; (2) sheet material quality improvement is needed for high efficiency cells; (3) 20% cell of this design is feasible with 10 ms bulk lifetime material; and (4) for achieving efficiencies higher than 20% new cell designs including thin cells with light trapping and back surface field should be considered

THYMOQUINONE: THE EVALUATION OF ITS CYTOTOXIC POTENTIAL, EFFECTS ON P53 STATUS AND THE CELL CYCLE IN VARIOUS CANCER CELL LINES

Cancer is a group of diseases that are the second leading cause of human mortality in the United States. Discovering new therapies is vital to conquer cancer. Thymoquinone (TQ) is found in the plant Nigella sativa. TQ was found to be cytotoxic to the human ovarian cancer cell lines PA-1, CAOV-3 and SKOV-3, which have varying p53 status. PA-1 cells were the most sensitive, indicating that TQ was effective against cells having wild-type (WT) p53. Western blots indicated an increase in p53 in cell lines having WT p53. TQ when given concurrently with cisplatin resulted in antagonism for PA-1, A172 and H460 cell lines. Sequential exposure to TQ followed by cisplatin resulted in synergy or additive effects in these cell lines. Sequential exposure to cisplatin followed by TQ resulted in additive or moderate antagonism in these cell lines. Concurrent exposure to TQ and paclitaxel showed synergy in PA-1 and H460 cells. Sequential exposure to TQ followed by paclitaxel resulted in synergism or antagonism in A172, PA-1, and H460 cells. Paclitaxel followed by TQ resulted in antagonism or synergism in these cells. These results demonstrate that TQ has a potential as an antineoplastic agent and may affect p53 levels

Of Single Nucleotides and Single Cells: Charting the Genotype-Phenotype Map at High Resolution Using \u3ci\u3eDrosophila melanogaster\u3c/i\u3e

Understanding the mechanisms by which genetic variation brings about phenotypic variation is essential for understanding variation in complex traits. Drosophila melanogaster is a powerful model organism for such studies. Flies are easy to raise in the laboratory under controlled genetic and environmental conditions and many genetic tools are widely available. To chart the genotype-phenotype map, we need to study how individual genetic variants contribute to phenotypic variation, as well as how environmental perturbations influence gene expression. Regarding the former, I generated single nucleotide substitutions in Obp56h in a common genetic background. Obp56h, a member of the Odorant binding protein multigene family, is a small gene in a favorable genomic location for CRISPR-Cas9 mediated deletion. After deletion, I reinserted the gene at the endogenous locus with individual allelic variants chosen from those segregating in a wild-derived inbred population to produce five lines varying at single nucleotides in a common genetic background. Different alleles, both within and near the gene (potentially regulatory) and both common and rare, have different, large effects on organismal fitness traits as well as on genome-wide coregulated ensembles of transcripts. These effects are at the level of mean and microenvironmental variance in both fitness traits and the transcriptome. However, these alleles have only small effects on fitness traits in the wild-derived inbred population indicating that the effects of individual alleles can be context-specific and are perhaps suppressed in natural populations via epistatic interactions. Next, I studied how acute cocaine consumption and developmental alcohol exposure affect the transcriptome at single-cell resolution. The Drosophila brain is small, allowing for comprehensive whole-brain studies. Further, previous studies have characterized effects of acute cocaine consumption and developmental alcohol exposure on flies, which resemble those in humans. Single-cell RNA sequencing revealed that the transcriptomes of cells in the fly brain are affected in a cell-type and sex-dependent manner after the flies consumed fixed amounts of cocaine or are exposed to developmental alcohol exposure. These effects are sexually dimorphic, with males showing a greater degree of differential expression and are particularly prominent in glial and mushroom body cells. Developmental alcohol exposure leads to a similar, but different, sexually dimorphic and cell-type dependent pattern of differential expression as cocaine consumption. Some mechanisms are shared between the experimental paradigms indicating common processes. The strategies used in the studies described in this dissertation can be generally applied to explore genotype-phenotype relationships at high resolution